Immigration would solve any drop in birth rates but it's also important to increase TFR. We shall see if the current raft of measures is going to be helpful
Immigration is a thorny problem. China is
mostly populated by 1 major ethnicity. If it starts getting more immigrants from around the world it could destabilise the country, which is a big no-no for the CPC.
As you later said, I think maybe only SEAsians could be considered, and even then maybe Japan and S.Korea as they would already be rich and thus are highly educated.
IMO it is a bit early to talk about any potential immigration. The Chinese Gov has already started taking serious measures to ease the pressure on children and parents. I am expecting a lot more measures to be rolled out in the near future.
We will probably need to wait max 3-4 years to see if there is any effect. If it doesn't, then thats when the immigration will be seriously considered.